Macroevolution:
Systematics, Classification, Origin of Life, Paleontology,
Biogeography,
Coevolution
Evolutionary
Biology (BI 25) Lecture Notes
Systematics -study of evolutionary
relationships of organisms
Taxonomy - Science of biological
classification of organisms
Goals of Taxonomists
1) Reveal evolutionary relationships
between organisms
2) Describe pattern of evolutionary
relationships from primitive to advanced
3) Find ancestors along with
input from paleontology
4) Constantly re-evaluate previous
classifications
Current System: The Taxonomic/Linnaen
Hierarchy for a Biological Classification
Characteristics of the
system
System Is Hierarchical
Binomial Classification
What is a classification?
Classification is a system with
categories that contain similar organisms which descended from
a common ancestor, reflects
a phylogeny or genealogy, reconstruction of relationships among
taxa and groups they belong
to
A classification is also considered
to be a monophyletic group of taxa
Composed of Categories
Examples
Kingdom, Phylum,
Class, Order, Family, Genus, Species
Categories are arranged into
a hierarchy with most inclusive group at top and least inclusive at the
bottom
Example
Kingdom (Animalia)
Phylum (Chordata)
Class (Mammalia)
Order (Primates)
Family (Hominidae)
Genus (Homo)
Species (Homo
sapiens)
Taxon - formal name for each
category
Examples
Animalia, Chordata, Mammalia,
Primates, Hominidae, Homo, Homo sapiens
Printing conventions
Genus capitalized, species
not capitalized
Both genus and species
italicized or underlined
All other taxonomic
unit names capitalized, but no distinctive print style
How are classifications produced
Homology
Fundamental concept to evolution
and classification
Definition - a structure possessed
by members of 2 or more taxa that was shared by a common ancestor
Examples
Individual bones of the
vertebrate forelimb - humerus, radius, ulna, carpals, metacarpals,
digits (or phalanges) - each are homologous structures found in many
vertebrates
bones of the pelvic girdle
of vertebrates (illium, ischium, pubis)
Chitinous exoskeleton of
arthropods
Feathers of birds
Hair and mammary glands
of mammals
Convergent evolution - homoplasy,
when two or more species share characters but did not descend from
a common ancestor (examples
- wings of insects, birds, bats, pterosaurs; fusiform shape of cetaceans,
sharks, penguins, icthyosaurs;
Australian mammals)
Parallelism - another form of
homoplasy, similar features evolved in closely related species but
independently of each other,
intermediate ancestor was different from both descendants,
some ant-eater like features
have evolved in different groups of mammals not closely related to the
anteater
Types of characters used in taxonomic
research
Qualitative characters (qualities
of an organism's phenotype)
Behavioral characters
Quantitative characters (measurements)
Biochemical genetics
Immune responses (antigenic
distances), allozymes, nuclear DNA, mtDNA, clDNA, other
Assess character state
primitive - reveals evidence
of the ancestral condition
derived - reveals evidence
of recent modification
Schools of Taxonomy
Phenetics
use of mathematical measures
of similarity - produces a similarity matrix between taxa
| Taxa |
A |
B |
C |
| A |
- |
.7 |
.2 |
| B |
|
- |
.2 |
| C |
|
|
- |
uses as many characters as
possible (don't worry about convergence)
produce dendrogram depicting
relationships, uses various clustering algorithms, based on
the similarity matrix
Example - Schnell (1970) produced
classification of Charadriiform birds based on external
and skeletal measurements
problems - too much emphasis
on total similarity, can not handle convergent or parallel traits
Cladistics or Phylogenetic Systematics
uses homologous characters
and rigorous character analysis
primitive characters = pleisiomorphic
derived characters - apomorphic
determined by character polarization
- finding out which one is primitive versus derived
Methods - compare with the
fossil record, outgroup comparisons, other
use of shared, derived characters
(synapomorphies) that define groups, produce cladograms
Evolutionary classification
mix of both philosophies, use
homologous characters and emphasize overall similarity,
emphasizes the amount of morphological
change during construction of phylogenetic relationships
uses shared derived characters,
uses overall similarity in assessing taxonomic rank
problems - character weighting
plays an influential role in defining taxa
Origins
Origin of the Universe
Cosmology - study of the origin
of the universe
Big Bang - Big Bang - single
origin, expanding universe, time has a single beginning and the universe
willeventually end in a single collapse
11 - 20 BYA - big bang (all
matter is condensed into a small area, followed by an explosion
Immediately after explosion
- fusions of small atoms into larger atoms
10 BYA - galaxies form, stars
are formed and are burning, some explode into supernova
Hale-Bopp - one example of
a piece of the big bang floating around the universe
Evidence
galactic expansion - Doppler
shift, light waves from distant galaxies indicated a shift away from
the earth
black body or fossil radiation
- low temperature radiation from the galaxies and the stars, predicted
from an expanding universe which had a very high original temperature
and cooled down
radio waves - associated
with the presence of galaxies, increase in the number of radio waves/galaxy
is related to the light year distances and time of origin of a galaxy
hydrogen and helium proportions
- proportion of hydrogen and helium in the universe can not be due
to synthesis by galactic stars, had to be synthesized by a big bang
Continuing search for evidence
from NASA
Mars
Rover Mission
Overview
of the mission - search for water, characterize rocks, etc.
Cassini
Mission to Saturn
Overview
of the mission - investigate rings, planet Saturn and the Moons,
especially Titan which has is the only moon with its own atmorsphere
Oscillating Universe - series
of big bangs, time has no beginning and no end, time is infinite, universe
oscillates between expansions
contractions (big crunch),
contractions caused by gravity which can reverse expansion of matter
Steady State - unchanging universe
except that as hydrogen diminishes in supply it is replaced by hydrogen
from an unknown source,
at higher levels - old galaxies
are replaced by new galaxies
Origin of the Planets and Solar
Systems
Collision theory - a second
star nearly collided with our sun and its gravity pulled out materials
from the sun
which eventually became
the protoplanets
Dust cloud or condensation
theory - large condensing mass of material in the center of a cloud
became the sun,
peripheral masses never
reached critical temperatures to becomes suns, instead became protoplanets
Earth Formed 4.5 Billion Years
Ago
5 BYA - origin of our solar
system and the Milky Way Galaxy
Particles revolve around
a proto-sun
Dust condenses
asteroid belts
planetessimals - collide
and compress
4 BYA - planets form and
revolve around the sun
Earth's atmosphere - dominated
by hydrogen, methane, water, ammonia, nitrogen, carbon monoxide
Where did oxygen come from?
-
UV irradiation of
water in the upper atmosphere, split water into hydrogen and
oxygen
-
2 - 3 BYA, appearance
of first autotrophs - blue-green algae
Earth as it is today
Crust - 3 rock types
igneous crystallize out
of molten magma pushed up to the mantle
sedimentary rocks are
the results of erosion of igneous rocks, becomes the geological
debris
that settles into rivers,
lakes, streams, oceans
metamorphic rocks are
igneous or sedimentary rocks that underwent changes due to
chemical reactions,
heat, pressure
The moving crust - plate tectonics
crust floats/moves over the mantle
lava floats up to the surface
and moves plates/continents apart - creates mantle currents
Lava
from the Kilauea Volcano, Volcanoes National Park, Hawaii (28 May, 2003)
Digital
video of lava flow from Kilauea Volcano, Volcanoes National Park,
Hawaii (28 May, 2003)
2 adjoining plates slides past
each other (Pacific plate carrying section of California northward along
the San Andreas fault)
2 plates collide, one plates
goes under the other (Pacific plate plunges into the mantle where it meets
the North American
plate at the Aleutian Islands,
causes volcanic activity and uplifting or mountain building - Aleutian
Islands, Andes
Mountains where Pacific plate
meets and plunges under the American plate in South America)
Major land masses
Pangea - oldest, all continents
connected
Laurasia - split of Pangea,
this contained the northern continents
Gondwanaland - split of Pangea,
this contained the southern continents
Origin of Life from chemicals
Nature of Early Earth
Composition of original atmosphere
Primarily nitrogen gas, carbon dioxide, water
Secondarily hydrogen sulfide, ammonia, methane
Debatable whether free hydrogen gas was present
Termed a reducing atmosphere
Requires less energy to form carbon molecules
Free oxygen gas absent
Available chemicals - Water, H, O, C, N, S, P and Ca among others
Significant geothermal energy available
Presently shielded from UV radiation by ozone layer
Prompted chemical reactions of atmospheric materials
Formed complex molecules
Stored energy in covalent bonds
Life may have originated in deep-sea hydrothermal vents
Origin of Life 5 Hypothetical Stages - Hypothetical Sequence
1) Formation of organic molecules
from inorganic materials
a) abiotic synthesis of organic
compounds (Oparin - Haldane model, confirmed by Miller-Urey
experiments) reducing atmosphere,energy,
water,
b) Panspermia - organic molecules
could have come from outer space, Murchison
meteorite contained amino
acids that did not originate on earth, all amino acids
were very similar to ones
produced in the Miller-Urey experiments
2) Polymerization of organic
molecules to make more complex compounds
dehydration synthesis needs
energy and concentrating organic compounds - cyanic
condensing agents (cyanamide,
cyanogen, cyanic acid, etc..) produce peptide bonds in
aqueous solutions, could have
occurred on clays
anhydrous production - heat
can remove water in the absence of condensing agents
3) Formation of a barrier to
separate inside of proto-cell from outside, could have formed through
membranous droplets or vesicles
Types - coacervates
colloidal particles separate
out of solution into droplets under certain
conditions (temperature,
pH, etc.), electrically charged water molecules become
tightly bound to charged
molecules and or charged particles, water molecules
form a film-like barrier,
separates internal chemistry of the droplet from the outside (Oparin
1957, 1971)
Types - proteinoids - dry amino
acids can be polymerized, forming protein-like molecules
(proteinoids) when heated
and allowed to cool in water, coolling water can produce microspheres
which separate out of solution,
microspheres have two-layered boundary which is osmotically
active, are gram - when
stained, internal chemistry of the droplet from the outside, can undergo
processes similar to fission
and budding under certain conditions (Fox 1965, 1980)
Types -liposomes - protocells
with a phospholipid bilayer membrane, under certain conditions
(addition of proteins, etc.)
boundary becomes increasingly selectively permeable
Importance to evolution of
life
selective permeability
isolation of external and
internal environment
small size increases probability
of chain reactions inside the cell (products of one reaction can be
the reactants of another)
membranes could have incorporated
peptides which acted as channels or pumps for other molecules, moving
them in and out of the droplet
4) Production of enzymes necessary
for energy in chemical reactions that take place inside a cell but proteins
are made from instructions from
RNA which receive instructions from DNA (transcription and translation)
-
where did the catalysts come
from? First - need a self-replicating system
Probable answers: 1) rRNA replicates
itself and controls chemical reactions without help of other proteins,
RNA world, based on work
by Cech (1987), found that rRNA could make copies of itself without
the help from proteins
Probable answers: 2) proteins
or protein-nucleic acid combinations
5) Evolution of the genetic code
(relationship between 20 amino acides, DNA, mRNA and tRNA) - many
theories and alternatives explaining
the association between amino acids and their codons and anticodons:
a) triplet code may have evolved
from singlet or doublet code, a primitive triplet code or a codon quartet;
b) frozen accident - present
code evolved by chance, natural selection would have favored the code
with the least
amount of potential for
mutation (triplet code);
c) stereochemical hypothesis
is that the code is the outcome of chemical relationships between amino
acids and
tRNA (little chemical evidence
for these relationships)
6) Evolution of metabolism based
on comparative studies, indicates that anaerobic metabolism preceded
aerobic metabolism,
Metabolism - reactions that
break down high energy carbon compounds similar to anaerobic glycolysis
may
have been primitive percursors,
had to occur under anaerobic conditions because there was little
oxygen in the atmosphere,
predetermined by the abundance of small molecules available, later
pathways evolved to handle
larger molecules, eventually gave rise to the Krebs cycle
Photosynthesis - some protocells
switched to reduction reactions with CO2 using H2S
and later H2O as
electron sources, released
them from a dependence on organic compounds as a source of energy,
although still heterotrophs
- this transition could have lead to the evolution of photosynthesis,
photosynthesis creates an
aerobic environment and organisms that have produced their own
sugars which could be made
available to other organisms, provides opportunity for evolution
of the Krebs cycle and create
more energy from the breakdown of glucose in advanced heterotrophs
Evolution Timeline for the Origins and Extinctions of the Major Groups of Organisms
Summary - see table above for specific
events
Proterozoic - age of the bacteria,
archaebacteria, first eukaryotes
Paleozoic - Cambrian explosion, origin of major phyla
Mesozoic - age of dinosaurs,
origin of birds, mammals
Cenozoic - replacement of forests
by grasslands, evolution of humans, mass extinctions caused by
humans
Paleontology
Fossil - term coined by Agricola
in the 16th century, derived from fossilis - to dig up
Modern Definition of fossils
Stahl (1985) - "Every trace
of the physical existence of an extinct organism is considered a fossil
and
regarded as potentially helpful
in determining the history of an ancestral line."
Examples of fossils
fossilized bone, animal body
parts, plant parts, etc.
imprints of organisms or their
body parts
footprints
burrows
corprolites - fossil feces
eggshells and nest imprints
wounds or other damage caused
by predators are left on some organisms
fossil remains in the intestines
of organisms
gastroliths - fossil gizzard
stones in some reptiles
fossil insects in amber
(bark beetles in amber from Museum of Comparative Zoology - Harvard Univ.)
Processes of fossil formation
sedimentation - organisms die
near shorelines or wet areas, become buried in mud and covered by silt and
sediments
cold storage: frozen fossils
- frozen in ice (Wooly Mammoth, ICE MAN)
petrification
mineralization - minerals seep
into tissues or hollow spaces of bones (silica or calcium carbonate
amber = chemically altered resin
of ancient trees
bogs - aseptic preservation in
water hostile to bacteria and other organisms
tar pits - organisms caught and
drown in tar pits, become covered over
waxy hydrocarbon covering caused
by oil flows
mummification
lava flow catches an organism
dessication or sandstorms in
the desert
Limitations of the fossil record
bias towards organism preserved
by sedimentation, living near water
small organisms are poorly preserved
birds with hollow bones are poorly
preserved
soft parts of organisms are rarely
preserved
Dating Fossils
Radiometric dating - decay of
radioactive materials (decay at a constant rate)
Carbon 14 method - ratio of C14/C12,
c14 has a half life of approximately 5,600 years, used for rocks approximately
50,000 years old
Potassium-Argon, isotope of potassium
decays into inert argon, used for aging fossils under 0.5 million years
old
Uranium (U238 isotope) -Lead
(PB 206) method - calculate the ratio of lead/uranium, 1/2 life of 4.5 billion
years, used to age rocks in billions of years
Index fossils - widely distributed
fossils that are restricted in time and their time of existence is well
known, can be used as markers
Paleomagnetic Scale (from Newell - Chapter 9)
variation in the earth's magnetic
field, fields move westward on a regular basis, revolve around the axial
poles once/10,000 years, iron particles in rocks are like frozen compass
needles which can be used to age rocks
Oxygen Isotope Method (from Newell - Chapter 9)
evidence from glacial and interglacial
periods in the earth's history, based on Oxygen 18 (O18), O18/O16 ratio
is higher in sea water than in fresh water, increases with temperature
and salinity, picked up by aquatic invertebrates living in sea or freshwater,
glacial and interglacial periods are recorded in the oxygen ratios in
these invertebrates,
Varves (from Newell - Chapter 9)
summer versus winter sediments
in lakes and ponds, leave light (summer) and dark (winter) layers, similar
stratification in ocean sediments, caused by plankton blooms, similar
banding patterns in ice and glaciers
Coral (from Newell - Chapter 9)
tides acts as brakes to the
rotation of the earth, slowing down its rotation, can be picked up in
the annual growth bands of corals, each growth band represents one year
and is composed of growth lines of equivalent to one day, Wells found
that the number of growth lines per year was decreasing in fossil coral,
older coral had more growth lines, younger coral had fewer lines
Some Important Trends in the Fossil
Record
Horse
Evolution: woodland browser to grazer on the open savanna
4 toes and clipping teeth to
one toe and grinding teeth
Human Evoltuion: arboreal tree
climber - edge species (knuckle walker) - bipedal movement on the savanna
Evoltuion of the vetebrate jaw
- from gill arches
Evolution of the mammalian ear
- from jaw and skull bones
Evolution of size - titanotheres
Molecular Paleontology
Study of fossil or ancient
DNA (aDNA), DNA found in fossils
Examples
Frozen Wooly Mammoth about 40,000
years old
Sabre-toothed
Cats, 10,000-38,000 year old DNA from the La Brea tar
pits, links these cats with Felidae within the Carnivora, suggests independent
evolution of sabre teeth in the Nimravidae (another extinct carnivore family
related to the Felidae)
Insects (termites) preserved
in amber, 40 million years old, fossil termite DNA very similar to modern
species
Weevils, 120 - 135 million years,
represent ancient group of conifer-feeding beetles, among the oldest DNA
found
Fossil Magnolia leaves, 20 million
years old
Extinct horses - Quagga, extinct
species closely related to Zebra, 140 years old
Mummified soft tissues of Moas,
3,300 years old, Moas and Kiwis lived together in New Zealand,
Moas more closely related to
each other Moas and not to Kiwis which are more closely related to other
ratites
Ancient Human DNA, rib sample
of a Neanderthal infant, similar to closely related Neanderthal mtDNA but
not modern human mtDNA, Neanderthals constitute a distinct group, separate
from modern Europeans, some evidence of variation among Neanderthal groups
in Europe, can not tell conclusively whether Neanderthals were replaced
by modern humans in Europe (via competition) or were consumed by modern
human gene pool via hybridization, more recent evidence suggests that Neanderthals
went extinct without hybridization
References
on Ancient DNA
General Technique
Scan specimens for DNA
PCR - make copies of ancient
DNA for analysis
Gel electrophoresis used to separate
DNA fragments by size and charge
Also being used on specimens of
recent species in museums
DNA extracted from 60-80 year
old Kangaroo rat specimens was similar to DNA of present populations
Evolution of the higher groups
Tied to differentiation of tissues
and cells during development, controlled by genes and proteins
Development involves position,
cells, cell differentiation into different tissues, influenced by uneven deposition
of maternal substances in the egg cytoplasm, gravity and genes regulating
developmental pathways
Homeotic changes or mutations -
gross aberrations in development and growth patterns, developing
cells lose positional information
Example - antennapedia mutation
in Drosophila - leg grows in place of an antenna
Hox genes Complexes
Homeoboxes - related DNA sequences
found in various locations in the Drosophila genome, produce homeodomains
which are proteins made up of 60 amino acids, regulate mRNA production and
genes that affect cell positioning and differentiation into different body
parts, similar Hox genes found in many different organisms (homologous hox
genes)
Examples
Hox gene for anterior - posterior
segmentation found in arthropods and vertebrates
Hox genes for growth of neuronal
axons in nematodes and vertebrates
Hox genes for growth of anterior
sense organs (eyes) and CNS in humans, fish, tunicates, mollusks,
insects, other
Allometry - different parts of
the body have different growth rates, leads to shape changes
Heterochrony - timing of growth
changes in different parts of the body, some parts grow while others do not
or grow later
Paedomorphosis - incorporation
of adult sexual features into larval or immature forms
Neoteny - retain traits of immature
stages in the adult
Study of Adaptation
Definitions
Trait - phenotypic adjustment
to the environment that has been selected for that function
Process - evolution and natural
selection for a trait that increases the fitness of individuals that possess
it
Problems
Idle Darwinizing - promoting
adaptive explanations without any evidence
Adaptationist program - assumes
each feature considered to be an adaptation is the result of natural selection
Examples of non-adaptive traits
Behavioral adaptation could be
due to cultural inheritance (learned) with no genetic basis
Neutral mutation, not adaptive,
could be the result of genetic drift
Trait may be an example of physics
or chemistry - blood is red because of hemoglobin structure but it is not
an adaptation
Genetic hitchhiking - a trait
is not adaptive but it is correlated with another trait that is an adaptation,
Atwood et al. (1951) monitored
the frequency of a non-functional his- allele and a functional allele
his+ in bacteria, they found that frequencies of both alleles increase
and decrease because they are linked to other mutations that increase
and decrease in the population
Phylogenetic history - trait
may have been passed on from ancestors,
wingless trait is not adaptive
(Futuyma 1998), remnant of history,
large fruits of tropical trees
were adaptations for dispersal by large mammals that are now extinct (Janzen
and Martin 1982)
Idle Darwinizing replaced by experimental
approach
Process of recognizing adaptations
- 3 steps
1) identify hypothetical adaptive
trait (biochemical, physiological, anatomical, behavioral) and the variations
of it that occur (or could occur)
2) develop a hypothesis or model
of the function of the character
3) design a study to test of
the hypothesis
Methodologies for recognizing adaptations
Complexity and ubiquitous nature
- structure is extremely complex and found among many different species
(Examples - lateral line of
fishes is sensitive to water pressure)
Design - function and design
of a morphological structure conform to laws of physiology, physics, chemistry,
biomechanics (Gleason 1952):
leaves of sage bushes in hot environments are divided into leaflets or
are easily torn along fracture lines to dissipate heat; larger populations
of birds and
mammals are found in colder
environments - Bergmann's rule,
extremities of animals in cold
environments are shorter compared to animals in warm areas - Allen's rule
Comparative method: compare the
trait across different species with different ecological requirements
Example
Darwin examined sexual dimorphism
and mating systems - ornate features of males are adaptations for either
female choice or male competition, based on the evidence that polygynous
species tend to be dimorphic compared to monogamous species, also polyandrous
species show reverse dimorphism
All examples of convergent
evolution (fusiform shape of aquatic animals, large size of mammals
in cold environments)
Harvery and Pagel (1991)
- found that large testes is an adaptation among primates, polygamous
taxa had relatively larger testes than monogamous taxa (produce more
sperm for more matings)
Experimentation: test the adaptation
under different experimental conditions, usually done by altering the trait
and subjecting it to different treatments
Example
Silberglied et al. (1980)
altered butterfly wing patterns (by painting them) to test if they really
provided camouflage or not
Kettlewell (1955) released
both morphs of the Peppered Moths in polluted woodlands, found that
dark form outsurvived the light form
Widow Birds (Andersson 1982)
- altered the tail length of males (shortened, lengthened, kept the
same), males with longer tails were chosen more often by females compared
to other males
Barn Swallows (Moller 1994)
- similar study and results
Life history strategies
semelparity - breed once during
lifetime (salmon, some insects)
iteroparity - breed many times
(annual plants)
age specific reproduction - delayed
maturation and breeding usually occurs early in life
(gulls, puffins, raptors, other)
optimal clutch sizes - balance
between many factors (number of eggs that can be produced
by a female, amount of food,
ability to feed young, other)
r selection - many young, no
parental care
k selection - a few young, extensive
and long period parental care
Biogeography
Study of geographic distribution
of plants (phytogeogrpahy) and animals (zoogeography)
describe patterns of distributions
explain patterns and evolution
of species
Distributions affected by several
factors
geology
ecology
historical events
Levels of study
Species
describe range (breeding, winter,
migration)
disjunctions in range
Examples
Osprey - cosmopolitan distribution
Seabirds - pelagic distribution
Spotted
Owls - disjunct distribution
Above species level - distribution
of higher taxa and species
describe distribution of a
group/taxon
describe patterns of distributions
compare patterns of different
groups to see if they are concordant, may reflect similar evolutionary
or historical events
describe how geographic distributions
conform to geographic barriers (mountain ranges, bodies of water, islands,
deserts, etc..)
describe the effects of isolation
on the evolution of taxa (Australia)
Some obvious patterns
Biogeographic Realms - broad
geographic areas with endemic taxa that evolved together, each area is characterized
by closely related taxa not (or rarely found in other areas)
| Realm |
Fishes |
Amphibians |
Reptiles |
Birds |
Mammals |
| Palearctic |
Carps |
Newts |
|
Larks |
Voles |
| Ethiopian |
Elephant Fishes |
Hyperoliid
Frogs
|
Chameleons |
Turacos |
Giraffes |
| Oriental |
Gouramis |
Rhacophorid
frogs
|
Uropeltid
snakes
|
Pheasants |
Treeshrews |
| Australian |
Lungfish |
|
Pygopodid
lizards
|
Bowerbirds |
Kangaroos |
| Nearctic |
Basses |
Plethodontine
Salamanders
|
Snapping
Turtles
|
Turkeys |
Pronghorn
Antelopes
|
| Neotropical |
Knifefishes |
Bolitoglossine
Salamanders
|
Whiptail Lizards |
Antbirds |
Guinea Pigs |
after Futuyma (1998)
Disjunct distributions
Marsupials - Australia and
South America
Camels and their relatives
- Middle East and South America
Biodiversity - Gradients
highest diversity of species
in the tropics, decreasing diversity towards the poles
Examples
thousands of species of birds
in the neotropics, hundreds of species in the nearctic
many more marine taxa in
the tropics compared to elsewhere
Explanations or hypotheses
degree of specialization
- special resources are less likely to be eliminated by climate change
in the tropics because climate is more constant in the tropics
greater productivity and
more resources in the tropics
evolutionary history 1 -
recent glaciation events lead to extinction of species in the high latitudes
or tropical environments may be less harsh and more favorable
evolutionary history 2 -
most species originated in the tropics, most of the earth covered by
tropics or sub-tropics, failure of many species to evolve adaptations
for cold
each explanation has its
own problems
Clines
Bergmann's rule - animals in
colder climates tend to be larger, decrease ratio of surface to body mass
(volume) and conserves heat
Allen's rule - animals in colder
climates tend to have smaller extremities, decrease ratio of surface to
body mass (volume) and conserves heat
Gloger's rule - animals in
the tropics tend to be more colorful while organisms in colder environments
tend to be paler
2 Explanations of geographic distributions
1) Dispersal - organisms move
and disperse into new areas
strongly tied to vagility (ability
to move)
winged organisms (bats, birds,
insects)
wind-borne organisms like
flower pollen or fungal spores
hitchhikers, seeds on birds
or fruit-eating animals, special attachments like burs on seeds
Paleo examples
human colonization of North
America from Asia via Bering land bridge, also elephants
Camelidae - from North America
to Asia via the Bering land bridge
Great American Interchange
- Isthmus of Panama opens up land bridge between North and South America,
movement of mammals from south to north - fossil armadillos of South
America and modern armadillos in North America along with marmosets,
anteaters and opossums;
also dispersal of many species
from North into South America (raccoons, rodents, carnivores, horses,
camels), results in a larger movement of North American species into the
south than vice-versa (50% of southern genera
are North American in origin, less than 20% of northern genera South American
in origin)
More Recent examples
Drosophila colonizations
of Hawaii, older lineages of flies are found on the older islands and
younger lineages are found on the younger islands
Honeycreeper ancestors in
Hawaii
Darwin's Finches in the Galapagos
Islands
Cattle Egrets from Africa
blown over by storms to the Caribbean and into North America
Tropical American snakes
- 2 major clades of Xenodontine snakes (1 from Central America and 1
from South America) diverged about 40-50MYA, 9/10 genera in the Greater
and Lesser Antilles belong to the South American clade, must be due
to dispersal because the Antilles are geographic buds from Central America
about 65 MYA
Artificial introductions
Zebra
mussels
Pigs,goats, cattle and
sheep grazing
threats to Island
Fox on the Channel Islands, California
threats to native
plants of Hawaii
threats to Galapagos
Islands (summary from World Wildlife Fund)
Wild
Boar or feral pig
rats (Norway
Rat 1, Norway
Rat 2)
Insects
Japanese
Beetle 1
Japanese
Beetle 2
Hemlock
Woolly Adelgid - aphids that destroy Hemlock trees in North
America
birds (European
Starlings, House
Sparrows)
Plants (Purple
Loosestrife, Eurasian
water-milfoil, Common
Reed = Phragmites)
2) Vicariance - former large,
continuous range has been disturbed and split by local extinctions,
geological events, other factors
Examples
Pup fish of the southwest
US, live in desert where water dries up, restricted to isolated springs
Isthmus of Panama - separated
marine fauna of Caribbean and Pacific oceans (fish - gobies)
Continental drift and plate
tectonics, strands populations
Cosmopolitan and vicariant
distribution of the Ratites (Kiwis in New Zealand, Ostrich in Africa,
Rheas in South America, Emu and Cassowaries in the Australian region
- very old group originally in Gondwanaland that was broken up by
continental drift)
chironomid midges, most
species are found in South America, Australia and New Zealand and
a few in the northern continents, indicates a vicariant distribution
that began with Pangea followed by separation of Gondwanaland and
Laurasia and subsequent spitting of South America from Australia and
New Zealand (Brundin 1988)
Approaches to study of Biogeography
- explain why organisms are distributed in the present patterns that we observe
them
Historical - study of distributions
based on fossil record and systematics
fossil record tells us where
and when - important in understanding dispersal and
vicariant distributions
horses in North America -
fossil species lived in North America, went extinct and then modern
horses were introduced by the Spaniards during colonization, due to
dispersal
Tropical American and Asian
distribution of tapirs - relicts of a once widely distributed group
(also included North America and throughout Asia), vicariant distribution?
Marsupials - similar to Ratites,
current distribution is largely restricted to Australia with some species
in North and South America, fossils found in Antarctica indicate previously
broader distribution separated by continental drift and plate tectonics
Systematics - used in the absence
of fossil evidence
cladistic biogeography -
draw area cladograms, areas are based on the taxa that inhabit them
Ecological - based on current
or relative recent ecological variables that may determine a taxon's distribution
Island Biogeography - explain
the number of species on islands, small islands have fewer species than
similar size patches on the mainland, due to an equilibrium (MacArthur
and Wilson 1967) between the number of colonizing species and the number
of species that become extinct on the island affected by area of the island
(larger islands have more species)
affected by the distance from
the mainland (more distant islands have fewer species)
affected by speciation rate
(if this is low then the number of species will be low)
affected by extinction rate
(if this is high then the number of species will be low)
interspecific interactions
on islands
predation - rats, cats, mongooses,
snakes, Predatory snail on the island of Moorea in the South Pacific
caused the extinction of other land snails (Murray et al. 1998)
interspecific competition
12 species of white-eyes
are distributed among islands off Papua New Guinea, no island has
more than one species
3 species of honeyeaters
are distributed over the island of Papua New Guinea but only occur
in pairs that are separated by altitude (Diamond 1975)
Coevolution
definition - reciprocal genetic
changes in 2 or more species
common examples
predator/prey - predator kills
and eats prey
herbivore/plant - herbivore
eats plant
host/parasite - host is adversely
affected and the parasite benefits
mutualism - both species benefit
competition between 2 or more
species
Predator/prey and Herbivore Plant
3 Consequences
Arms race - change in prey
species followed by change in predator species followed by change in prey..........
Stable equilibrium
Extinction of both species,
usually one goes first followed quickly by the other
Genes
single gene changes in each
species
polygenic changes in each species
Costs of adaptation
adaptations for predator or
herbivore avoidance may interfere with other body functions or adaptations
Corey et al (1985) chemical
defense in some plants increases total energy budget,
Dacosta and Jones (1971)
- cucumbers produce compounds for resistance against spider mites but
attract leaf beetles
predators -handling one species
of prey more efficiently may decrease the handling efficiency of other
prey species
Parasitism
Types of parasites (based on
virulence, the ability of the parasite to reproduce and inflict
damage to the host causing
death or inability to reproduce)
virulent - causes serious problems
for the host in a short period of time
avirulent - no problems for
the host
Host Strategies
evolution of immunity
lead a solitary existence (social
or colonial breeding species of birds experience higher rates of parasitism
than solitary species
behavioral adaptations - preening
by birds and mammals
allopreening (different individuals
preen each other)
autopreening (same individual
preens itself)
Parasite Strategies
infect but not kill host -
obtain benefits from the host but keep it alive so parasite can breed
as long as possible
kill the host because the eggs
or other stages are not released until the host is dead
Example of virulent species
Adaptation of parasites to
their hosts - Ebert (1994) studied protozoa in Daphnia, found that Daphnia
with higher numbers of parasites were more likely to infect other Daphnia
than ones with lower numbers of parasites
Ebert (1994) also found through
lab experiments that parasites were more successful parasitizing individuals
from their own or nearby populations than ones from distant populations,
parasites were better adapted to Daphnia from their home range than to
other Daphnia that they had never been exposed to
Adaptations by the hosts -
1950's introduction of European rabbits becomes pests in Australia, virulent
myxoma virus introduced to kill rabbits, kills most of them but a few
were resistant and a new population of rabbits developed resistance, also
some strains of the virus evolved lower virulence (Fenner and Ratcliffe
1965, May and Anderson 1983)
Mutualism
Douglas (1994) - several examples
of prokaryotes that invaded and live inside eukaryotes, both species derive
some biochemical benefits
Nilsson et al. (1985) - hawkmoth
with a long proboscis is a pollinator for a Madagascar white orchid with
a long tubular flower, goes for the nectar at the base of the flower
Hummingbirds, Sunbirds, White-eyes,
other avian nectarivores, insects, bats and other mammals that feed on plant
nectar and spread plant pollen, most species are tropical and prefer one
species of plant, prevents crosspollination
Problems with stability - one
species has the potential to over-exploit the other
Examples
Pellmyr et al. (1996) -
different species of yucca moths lay their eggs in the yucca plant
and consume seeds while adult moths are also pollinators, some species
do not pollinate but only consume
Futuyma (1998) - some bees
chew a hole in the base of the flower and extract nectar without ever
coming into contact with the flower's anther
Futuyma (1998) - C. formicifera
- orchid that mimic female sex pheromone and is visited by males that
copulate with the plant, insect pollinate but receive no benefit,
in fact they waste sperm and energy
Competition
Competitive exclusion - if 2
species occupy the same niche, utilize the same resources, one
species outcompetes the other
and the loser becomes extinct
Gause (1934) - laboratory experiment
with 2 species of Paramecia (P. aurelia, P. caudatum), P. aurelia outcompeted
the P. caudatum and the P. caudatum went extinct
Introductions - Pianka (1994)
summarizes several cases of introductions where foreign species have outcompeted
local endemic forms which lead to their extinction:
European Fox and the Dingo
introduced into Australia lead to the extinction of the Tasmanian Wolf,
native Hawaiian birds went
extinct after introduction of the House Sparrow
Character or ecological release
- species exhibit greater morphological variation in areas that
lack competitors (especially
marked on islands that lack mainland competitors, sometimes referred to
as incomplete biotas)
Van Valen (1965) - measurement
variation in bill length and bill width (coefficient of variation) 6 species
of birds on islands was greater than variation on the mainland
Melanerpes striatus (woodpecker)
in Hispainolo exhibits sexual dimorphism in beak and tongue size but other
Melanerpes species on the mainland which coexist with other woodpecker
species lack sexual dimorphism (Selander 1966)
Crowell (1962) found that 3
species, Northern Cardinal,
Gray Catbird,
White-eyed Vireo,
all occupied a wider range of habitats and foraging niches than conspecifics
on the mainland
Morse (1970) found that the
Northern Parula
Warbler and Myrtle Warbler
expand their habitat utilization and plasticity in foraging in the absence
of Black-throated Green Warblers on islands off the coast of Maine
Cocos Finch - on Cocos Island,
eats a wider variety of foods and has greater morphological variation
than other Galapagos finches on the Galapagos Islands which coexist with
other species
Coexistence - 2 or more species
are able to coexist, exploit the same resources differently
Occupy different niches - resource
partitioning
MacArthur (1958) - warblers
of eastern North America occupy different feeding niches in boreal (spruce
fir) forests
Diamond (1975) - fruit doves
in Australasia, larger fruit doves feed on larger fruits on larger branches
and smaller fruit doves feed on smaller fruits, also feed at different
areas on trees
Character displacement, term
coined by Brown and Wilson (1956), species are different
when they are sympatric to
avoid competition but allopatric populations are more similar morphologically
to each other
Examples
Vaurie (1951) studied
2 Old World (East Asia) species of Nuthatches(Sitta tephronota,
S. nuemayer) - very similar bill measurements and face pigmentation
in allopatry but strikingly divergent in sympatry
Galapagos finches - Geospiza
fortis and G. fuliginosa, same beak size (depth)when they are allopatric
but have different beak sizes when they are sympatric, G. fortis is
larger than G fuliginosa in sympatry (Grant 1986)
Sticklebacks in Canada,
sympatric species live in lakes and differ in several morphological
measurements (gill rakers, body shape, mouth morphology, etc.), in
lakes where there is only one species, the measurements are intermediate
between those of sympatric species (Schluter and McPhail 1992)
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